The processes so far known for producing said (2R,3S)-3-amino-1,2-oxirane comprise starting with L-phenylalanine, reducing the carboxyl group thereof to an alcohol function, reoxidizing the same to an aldehyde function, and thereafter 1) directly causing formation of the epoxide using a dimethylsulfonium methylide (J. Org. Chem., 1985, 50, 4615; J. Med. Chem., 1992, 35, 2525), 2) converting the aldehyde to the corresponding olefin by the Wittig reaction and epoxidizing the olef in using m-chloroperbenzoic acid (J. Org. Chem., 1987, 52, 1487; J. Med. Chem. 1992, 35, 1685), 3) reacting the aldehyde with trimethylsilylmethylmagnesium chloride, converting the resulting trimethylsilylalcohol to the corresponding olefin by treatment with trifluoroboron and, as in the method 2) mentioned above, conducting epoxidation using m-chloroperbenzoic acid (EP 0532-466 A2, U.S. Pat. No. 5,514,814) or 4) converting L-phenylalanine to the diazoketone form, degradating the same with hydrochloric acid, reducing the resulting .alpha.-ketone with NaBH.sub.4 and treating the resulting chlorohydrin with a base to give the epoxide (J. Med. Chem., 1994, 37, 1758), among others.
Meanwhile, there is no precedent technology for producing (2R,3S)-3-amino-1,2-oxirane compounds represented by the general formula (8) starting with a (2S,3S)-3-amino-1-chloro-2-hydroxy-4-phenylbutane compound or a (2S,3S)-3-amino-1,2-oxirane compound as in the process of the present invention.
Referring to the above known processes, the process 1) is disadvantageous in that it is necessary to use the sulfur compound in large amounts in the step of epoxide formation, the methods 2) and 3) are disadvantageous in that it is necessary to use the peroxide, which is explosive, in large amounts, and the method 4) is disadvantageous in that it is necessary to handle the diazo compound, which is also explosive, and, in addition, the selectivity toward the desired (2R,3S)-chlorohydrin in NaBH.sub.4 reduction is low. Thus, every process comprises a step undesirable from the viewpoint of commercial scale practicing.